1231552991 has 4 divisors (see below), whose sum is σ = 1231673184. Its totient is φ = 1231432800.

The previous prime is 1231552979. The next prime is 1231552999. The reversal of 1231552991 is 1992551321.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1992551321 = 421 ⋅4732901.

It is a cyclic number.

It is not a de Polignac number, because 1231552991 - 2²² = 1227358687 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1231552999) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 43130 + ... + 65751.

It is an arithmetic number, because the mean of its divisors is an integer number (307918296).

Almost surely, 2^1231552991 is an apocalyptic number.

1231552991 is a deficient number, since it is larger than the sum of its proper divisors (120193).

1231552991 is a wasteful number, since it uses less digits than its factorization.

1231552991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120192.

The product of its digits is 24300, while the sum is 38.

The square root of 1231552991 is about 35093.4892964493. The cubic root of 1231552991 is about 1071.8920119256.

The spelling of 1231552991 in words is "one billion, two hundred thirty-one million, five hundred fifty-two thousand, nine hundred ninety-one".